Method of coagulating polyvanadic acid salts



by th'e use of chemical precipitating agent s;

Patented Oct. 21, 1952 UNITED STATES PATENT or fice METHOD OF COAGULATINGPOIQYVANADIG AGID SALTS-t i it Tom S; Perrin; Pain'esville, Ohio, assignon'toDia mond Alkali Company, Cleveland, Ohio; a'corporation of Delaware NoeDrawing. 3 Application November:,1,,19 49, ScrialNo. 124,954

1 v This invention relates" to a method'oi coagulatingcpolyvanadicacid salts and more. particularly relatest'o'amethod'for'polyrneriaingimetavanad ic' acid and coagulating polyvan'adic acid salts.v

derived therefrom;

Vanadium is' customarily'extracted from ores containing'vanadiu-m compounds'associated with otherheavy metal compounds by roasting the ore with alkali'es, suc'h'as sodaash; and, leaching the oreroast' with water 'to obtain: a: solution of alkali metal salts of "hydrous"- oxidic' vanadium acids, such=asHVO's, HzViOs, and'salts' offheavy metal oxide acids, from which 'solution' the heavy: metal salts are removed by fractional'crystallizationtor a" co-pending applicationpserz'No. 59,935., filed-November 13, 1948; in'thename of the present" inventor and anotherfflnow Patent: 'No'. 583,591 dated January*29;' 1952, there-is described a process for the separation of salts" of hexametavanadic acid from-solutions ofrsoluble' chromate' salts, in which process the chromium and vanadium containing ore is'-roasted"withian alkali; such as sodium carbonate; after which,

the ore roast is leached with water and the vanae dium removed from the leach liquor by precipitation of ilead l vanadate "along with some lead chromateiiusing lead sulfate as" the precipitant: The

leadnvanadate lead chromate precipitate is then decomposed :with sulfuric acidto regenerate lead" sulfate as an insoluble precipitate and: to form and :chromic' acid in" the acid" extract solution;

The presentfinvention is particularly applicable totherrecoveryi of vanadium values from this lattersolutionor from vanadium containing process solutionsrzof 1a similar'chemical nature.

, It llBiS'fliIElBtOfOl'H been proposed to precipitate hydioustvanadium oxide" from acid solutions byr'adjusting the pH of the solution to' a point' within therrange of= 2-3, and heating the acid solution a temperature above 90 C. and up to the boiling point of thesolution; in order to' prevent precipitation of the hydrous vanadium oxide as a gummy h'ydrogel; It has also been proposed-r to precipitate a polyvan'adic; acidisalt,

suchras'the salt NazHzvton; or the analogous" ammonium :salt from acidified" solutions of al.- ka'li' metal vanadates at temperatures of the orderof 60 to 90 CL, and toemploy; an oxidizing -agent'to" eflect hydrolysis of vanadic acid, (HVQ) to the particularpolyvanadic acidsalt desired-c It has now been found" that in ordertto approach quantitative' recoveryof vanadium'values',"

6 Claims. (01. 23-51) the hydrous acid vanadium" oxides containedfin the above-described acid extractsand solutions of 'vanadates' must be completely oxidized to the highest state of oxidation for vanadium. In"

the prior art methods, the" IIBCESSltTfOITSHCh' oxidation hasrnot been" appreciated nor' has'it been" achieved and thus; the precipitation ofiithe'- particular polyvanadic acid salts by" prior-art methods does-nottapproach"quantitative'irecovery l0 -of' the lower-hydrous acidic" vanadiumoxide, do,

not react with the' other'acids 'in the acid ex tracts or acidifiedvanadatesolutions to form soluble lead compounds at the acid concentrations generally employed,- and in the contact time interval allowed for the reaction of the lead peroxide with thelower valent hydrous acidic vanadium'oxides. Moreoveiylead peroxide; while effecting the desiredox-idation of the-loweracidic vanadium oxide compounds;- does not introduce foreign" ions into theacid' extract solutionfrom which thepolyvanadic acid compounds areprecipitated and therefore does not affectthe'subse quent recoveryof other heavymetal salts or'acids,

from the solutions. This latter advantage is'of' importance in the recovery of'chromic' acids? or chromates from the mother'liquor obtained from' the decomposition of themixture'of'lead vana date and lead chromateprecipitates described hereinabove in connection with the co-pendin'g.

application Ser: No. 59,935 (Patent N o. 2,5833591) Thus, an oxidizing agent'such-as a hypochlorite;

disclosed in said, co-pending: application to be eflfective as'an' oxidizing agentin this connection",

introduces" the? chloride ion into the solution',. which chloride ion, upon extended contact with the solutions of. hexavalent chromium salts,.. re-

duces; these'salts to the trivalent state wherebyappreciable-amounts of trivalent chromium come.

pounds; are carried over into subsequentchemir cal processes, suchyas chrome; pigment manna- 1: facture, whereinthechloride.ionlorsthetrivalent;

chromium compounds'have a deleteriousefiect.

In addition to its function as an oxidizing agent, lead peroxide apparently acts as a polymerization promoter of outstanding efficiency for the metavanadic acid, whereby recovery of approximately 97% of the available vanadium in the form of hexametavanadic acid or salts thereof, such as Nazl-IzVeOn (which is a salt of hexameric HVOs minus one molecule of water), is possible. Furthermore, lead peroxide and its reduction products are readily separated from the acid solution containing the hydrous acidic vanadium oxides to be coagulated. Where such separation is made prior tothe coagulation of the polyvanadic acid salt, contamination of the coagulum or the mother liquor by the lead peroxide or its reduction product is avoided, and a clean separation of the polyvanadic acidcoagulum from the mother liquor and lead peroxide and its reduction products is effected.

The combined effect of lead peroxide in promoting polymerization of vanadic acid and in oxidizing lower acidic vanadium oxides is in marked contrast to the action of other oxidizing agents, for example, hydrogen peroxide ,or

sodium chlorate. These latter agents would be expected to exhibit the same chemical behavior in the acid solutions of hydrous acidic vanadium oxides that lead peroxide does, and, moreover,

to the same degree. Hydrogen peroxide and sodium chlorate, however, do not act as effectively in converting soluble hydrous acidic vanadium oxides to the insoluble polyvanadic acid salts referred to above, as evidenced by the fact that the maximum recovery of the polyvanadic acid salts obtainable by the use of these reagents is generally less than 50% of the avail-able vanadium contained in the acid solution, while when lead peroxide is used as the oxidizing agent and polymerization promoter, substantially quantitative precipitation of the available vanadium as polyvanadic acid salts results.

, More specifically, in the method of coagulating polyvanadic acid salts of hexametavanadic acid I in which initially a solution containing a mixture of hydrous acidic vanadium oxides is neutralized to a pH within the range of 1-3, and subsequently a coagulum of salts of said polyvanadic acid is obtained therefrom, the present invention is directed to the improvement which includes the steps of contacting a body of said solution prior .to neutralization with a mass of lead peroxide, to

oxidize reduced vanadium oxide compounds in said mixture to metavanadic acid, and separating said selution from said mass and the reduction products thereof. l

The vanadium-containing solution from which it is desired to recover the vanadium values may be derived from any suitable source of hydrous acidic vanadium oxides, such as the acid extract of a precipitate of insoluble vanadates, or an acidified solution of soluble alkali metal vanadates, or the like. It is preferable in practicing the method of the present invention .to concentrate, dilute, oradd vanadium compounds to the solution from which the hexametavanadic acid salt'is to be precipitated, in orderthat the concentration of V vanadium compounds therein, be substantially within the range of 16-20 grams per liter, calculated as HVOs, at the time the lead peroxide isbrought into contact with the solution. "It is also preferable to maintain a pH of less than one in the acid extract or acidified solution of vanadates at the time the lead peroxide is brought into contact therewith because of the greater solubilityof'the hydrous acidicvanadium .tion may suitably be of the order of 0.41.2 times the weight of vanadium, calculated as HVOs, in

the acid vanadium-containing solution. It is preferred, however, to use an amount of lead peroxide Within the range of 0.6-0.8 the weight of vanadium, calculated as HVOa.

The identity of the reduction product of the lead peroxide is not definitely established. The reduction product appears after contact with the acid vanadium-containing solution as a black or dark gray mass, insoluble at the preferred pH employed in the method of the present invention,

which properties are indicative atleast of the compound of PbzO, although some doubt exists of the existenceof such a compound. It is equally apparent, however, that the reductionproduct is not the lead compound identified in the art as PbO since this compound is soluble in, or reacts readily with, chromic acid; the reduction product obtained in the method of thepresent invention does not react with or dissolve in a mother liquor.

which includes chromic acid. 1

The mass of lead peroxide andqits reduction product, after being: brought into'contact with the hydrous acidic vanadium oxide-containing solution, and allowed to remain therein for a period of time sufficient to effect the oxidation of the lower valent vanadium compounds of such solution, is readily separated from the solution bysimple filtration. The lead peroxide may beregenerated from the reduction product by methods Well known in the art, such as by air oxidation, orv by oxidation with certain alkali metal salts, or by electrolytic oxidation.

After the separation of the mass of lead pe1'ox-.

ide and its reduction product from the body of solution containing the vanadium compounds, a base such as caustic soda, or an alkaline. sodium salt-, or alkaline ammonium salt, i added to the solution to adjust the pH to a point. Within the range of 1-2.5, preferably to a pH of the. order of 2. Coagulation ofthe polymeric sodium or ammonium hexametavanadic acid salt begins a1- most immediately. The solution'is heated, preferably to a temperature Within the range of approximately 60" C. to the boiling point of'the solution. during the coagulation of the disodium or diammonium salt of hexametavanadic acid, which may require from one-half hour to three hours to eifect substantially complete coagulation of the salt. The heated solution may also be agitated during the coagulation step since it has been found that heating and agitation effect a more. rapid agglomeration of the coagulum than is obtainable by either, heating the solution without agitation or agitating the solution Without heating. The separation of theidisodium or diammonium hexametavanadate from the mother liquor is readily efiected by simple filtration, the disodium or iammonium salt being in a readily filterable crystalline form as opposed to the gum-' my hydrogel which is obtained by certain of the prior art methods, referred tohereinabove. v

The vanadium =content of the hexametavan'a dete -salt may be mecovered *by' methods familiar In-order thatthose skilled i'n'the art may better understand the method of the; present invention and inwhat manner the same may be carried into effect," thefollowing specific examples are ofiered, in which the recovery of disodiumhexametavanadicacid-is used for illustration:

Example 1 A mass of a (Jo-precipitate of leadvanadatehand lead chromate, obtained from a process for the separation of chromium and vanadium values in chromate liquors by precipitation therefrom of the vanadium values as lead vanadate, together witha smallamount of lead chromate, is treated with sulfuric acid (45%) in ,antamountjequiva lent 1tot1l2. times the amount of lead in th'efipre'clp itate" to convert the chromate and vanadate rad-icalsof'theprecipitate to chromic and vanadic acids and form lead sulfate. The resulting solution having a pH of less than one is diluted with an equal volume of water, separated from the insoluble lead sulfate by filtration and concentrated to give a solution having 19.2 grams of vanadium per liter of solution, calculated as HVOs. The solution is separated into five portions, each of which is contacted with an amount of lead peroxide (PbOz) indicated in the table below, and stirred at a temperature near the boiling point of the solution for a period of about five minutes. Thereafter, the mass of reduced and unreduced lead peroxide is settled for a few minute and separated from the supernatant liquor by filtration. The pH of the hot solution is adjusted to 2 by slowly adding 50% sodium hydroxide to the solution While continuing the agitation. Thereafter, the agitation is continued While heating the solution to a temperature within the rangeof 90 to 95 C. for a period of three hours. The following results are obtained:

Wei ht Ratio, Percent HV a PbOz/HVOJ Removed Example 2 tions are agitated for a period of approximately three hours at a temperature within the range The concentration-of-lthe vanadic'acid; calcuf latedas HVOsQand the weight ratioof leadrperox idetto' vanadic acid (HVOs) i are the same-as described: in-. Example-2f the pH of the solution during the coagulation of -the disodium hexametavanadic acid-is maintained at 2 and'during the coagulation the solution is agitated and maintainediat atemperature of the order of; 90? :to

PercentHV or Time of Agitation llours Removed Employing the techniques of Examples 1-3, I

bodiments of the invention, the methods de-' scribed are not intended to be understood as limiting the scope of the invention as it is realized that changes therewithin are possible and it is further intended that each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing substantially the same results in substantially the same or equivalent manner, it being intended to cover the invention broadly in whatever form its principle may be utilized.

What is claimed is:

1. In the method of coagulating sodium and ammonium acid salts of hexametavanadic acid, in which a solution containing a mixture of hydrous acidic vanadium oxides and having a pH of less than 1 is neutralized with a base of the class of sodium and ammonium bases to a pH within the range of 1-3 to precipitate a coagulum of salts of hexametavanadic acid, the improvement which comprises the steps of contacting a body of said solution prior to neutralization with a mass of lead peroxide to oxidize reduced hydrous acidic vanadium oxides in said mixture and polymerize the metavanadic acid to hexametavanadic acid, and separating said solution from said mass and the reduction product thereof.

2. In the method of claim 1, the improvement which includes providing a mass of lead peroxide amounting to 0.4 to 1.2 times the weight of vanadium, calculated as HVOs, in said mixture.

3. In the method of claim 1, the improvement which includes the step of adjusting the concentration of vanadium, calculated as HVOa, in said solution to a point within the range of 16-20 grams per liter of solution, prior to adding lead peroxide to said solution. I

4. In the method of claim 1, the improvement which includes providing a mass of lead peroxide glow 7 man amount from 0.4 to 1.2 times the weight of vanadium, calculated as HVOs, in said mixture, separating said'mass and the reduction product thereof from said solution, and thereafter heating and agitating said solution at a temperature within the range of 60 C, to the boiling point of said solution for a period of one to three hours. 1 5. In the method of coagulating sodium and ammonium acid salts of hexametavanadic acid, in

which a solution containing a mixture of hydrous acidic vanadium oxides and having a pH less than one is neutralized with a base of the class of sodium and ammonium bases to apIl within the range of 1-3 to precipitate a coagulum of a salt of the class of disodium and diammonium salts of hexametavanadic acid, the improvement which comprises the steps of contactsalts of hexametavanadic acid which includes the 8 steps of contacting a solution comprising reduced hydrous acidic vanadium oxides having a pH of less than 1 with lead peroxide to oxidize said oxides, polymerizing the oxidized vanadium oxides present in said solution to hexametavanadic acid in the presence of said lead peroxide and its reduction product, separating said lead peroxide and its reduction product from said solution, neutralizing said solution with a base of the class of sodium and ammonium bases to a pH within the range of 1-3 to precipitate a coagulum of a salt selected from the group of disodium and diammonium salts of hexametavanadic acid.

TOM S. PERRIN.

REFERENCES CITED The following references are of record in the file of this patent: g

, UNITED STATES PATENTS Niunher Name Date 1,020,312 Saklatwalla Mar. 12, 1912 1,596,483 Frick Aug. 17, 1926' 1,621,038 Thews Mar. 15, 1927 1,733,700 Stevens et a1. 1 Oct. 29, 1929 2,130,579 Bowman Sept. 20, 1938 2,479,905 Cole et a1 Aug. 23, 1949 

1. IN THE METHOD OF COAGULATING SODIUM AND AMMONIUM ACID SALTS OF HEXAMETAVANADIC ACID, IN WHICH A SOLUTION CONTAINING A MIXTURE OF HYDROUS ACIDIC VANADIUM OXIDES AND HAVING A PH OF LESS THAN 1 IS NEUTRALIZED WITH A BASE OF THE CLASS OF SODIUM AND AMMONIUM BASES TO A PH WITHIN THE RANGE OF 1-3 TO PRECIPITATE A COAGULUM OF SALTS OF HEXAMETAVANADIC ACID, THE IMPROVEMENT WHICH COMPRISES THE STEPS OF CONTACTING A BODY OF SAID SOLUTION PRIOR TO NEUTRALIZATION WITH A MASS OF LEAD PEROXIDE TO OXIDIZE REDUCED HYDROUS ACIDIC VANADIUM OXIDES IN SAID MIXTURE AND POLYMERIZE THE METAVANADIC ACID TO HEXAMETAVANADIC ACID, AND SEPARATING SAID SOLUTION FROM SAID MASS AND THE REDUCTION PRODUCT THEREOF. 